Loudspeaker having annular diaphragm with double voice coil

ABSTRACT

A loudspeaker comprising an annular diaphragm including a vibrating portion having an arcuate shape in cross section, such as a shape of a fraction of a circle or an ellipse, and inner and outer peripheral support portions, voice coils attached to borders between said vibrating portion and said inner and outer support portions of the diaphragm and magnetic circuit means having concentric gaps for receiving said voice coils, respectively, to drive the diaphragm in phase with said voice coils.

United States Patent UNITED STATES PATENTS 11/1934 Parry .....179/115.5 R

Sotome 1 51 May 23, 1972' 1 LOUDSPEAKER HAVING ANNULAR 2,127,110 8/1938 Farrand... ....179/115.5 R DIAPHRAGM WITH DO VOICE 3,139,490 6/1964 Lyons ..179/l15.5 H COIL FOREIGN PATENTS 0R APPLICATIONS 1 1 lnvemon Hiromi m Hamamtsu-shi, Japan 4,312,103 5/1968 Japan ..179/115.5 vc

73 A Ni Gakki hlki I sslgnee gfig t is; Kabus Kmsha Primary Examiner-Kathleen H. Clafi'y Assistant Examiner-Thomas L. Kundert 22] Filed: Dec. 23, 1969 Attorney-Stevens, Davis, Miller & Mosher 121] Appl. No.: 887,534 [57] A loudspeaker comprising an annular diaphragm including a [30] Foreign Application Priority Dam vibrating portion having an arcuateshape in cross section, Dec. 30, 1968 Japan ..43/96579 u h a a h p f a fr n of a circle or an p and inner v V and outer peripheral support portions, voice coils attached to [52] U.S.Cl ..179/115.5Dv, 179/181 R,1.81/32R r r en s id vi r ing portion and said inner and [51 1m, (1,, outer support portions of the diaphragm and magnetic circuit [58] Field of Search ..l79/l 15.5 R, 1 15.5 DV, 1 15.5 VC, means having concentric gaps for receiving said voice coils, 179/1 15.5 H, 115.5 PS, 180, 116; 181/32 respectively, to drive the diaphragm in phase with said voice coils. [56] References Cited 1 Clairmfl Drawing Figures Patented May 23, 1972 3,665,124

2 Sheets-Sheet 1 l PRIOR ART INVENTOR.

H I ROMI SOTOM E ATTORNEYS Patented May 23, 1972 3,665,124

2 Sheets-Sheet 2 Fl G. 4

l2 l3 7 I? Fl 6. 6 FIG. 7

l N VEN TOR,

HIROME SOTOME BY @2754 9mm& W49

ATTORNEYS LOUDSPEAKER HAVING ANNULAR DIAPHRAGM WITH DOUBLE VOICE COIL BACKGROUND OF THE INVENTION The present invention relates to a loudspeaker having an annular diaphragm,

FIG. 1 shows an example of such loudspeaker, which is a hom-type loudspeaker comprising an annular diaphragm 1 supported at its inner and outer peripheries by a frame, a voice coil 2 attached to said diaphragm, a magnetic circuit 3 for driving said voice coil, a diaphragm cover 4 and an equalizer 5. The construction as shown in FIG. 1 can be also used in a direct-radiator loudspeaker having a larger diaphragm.

There is another type of diaphragm havingtwo or more voice coils. An example of such loudspeaker is shown in FIG. 2, which comprises a single cone-type diaphragm 6, two voice coils 7 and 8 attached to the diaphragmand magnetic circuit means 9, for driving said voice coils, whereby the diaphragm is driven by increased driving force throughout its whole surface so that divided vibration of the diaphragm is effectively reduced. The loudspeaker of this type may be so arranged that the two voice coils are separately driven by high and low frequency sound signals, respectively.

In the loudspeakers as shown in FIGS. 1 and 2, the borders between the support or edge portions and the vibrating portion of the diaphragm are not driven, so that the vibration of the support or edge portions effects the vibration of the vibrating portion of the diaphragm. If the vibration of the support portions acts on the vibrating portion in opposite phase, there may be caused deep dips in the frequency characteristics of the loudspeaker. The peripheral part of the diaphragm is weak since it is supported through the soft support portion, so that the diaphragm is liable to produce free vibration, resulting in turbulence in the frequency characteristics.

There is another type of loudspeaker, called as a dome-type loudspeaker, in which the border between the support or edge portion and the vibrating portions of the diaphragm is driven. An example of such loudspeaker is shown in FIG. 3, which comprises a diaphragm 10 having a dome-shaped vibrating portion, a voice coil 11 attached to the border between the vibrating portion and the support or edge portion and a magnetic circuit 12 for driving the voice coil. The loudspeaker of this type has such advantages that the vibrations of the vibrating portion and the support or edge portion are separated because the border between these portions is driven by the voice coil, so that the vibration of thesupport portion does not interfere with the vibration of the vibrating portion, and that the vibrating portion has increased strength due to the domeshape thereof. However, it has a disadvantage that a large vibrating area cannot be formed. If the vibrating area is increased, the diameter of the dome is also increased, whereby the effective weight of the diaphragm is increased and the mechanical strength of the central portion is decreased, thereby causing divided vibration of the diaphragm.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a loudspeaker which includes all of the advantages of the above having a voice coil attached to the border between the support or edge portion and the vibrating portion, and which excludes the disadvantages of the above loudspeakers.

In accordance with the present invention there is provided a loudspeaker comprising an annular diaphragm including a vibrating portion having an arcuate shape in cross section and inner and outer peripheral support portions, voice coils at tached to borders between said vibrating portion and said inner and outer support portions of the diaphragm and magnetic circuit means having gaps for receiving said voice coils, respectively, to drive the diaphragm in phase with said voice coils.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 are sectional views showing conventional types of loudspeakers;

FIG. 4 is a sectional view showing a loudspeaker according to an embodiment of the present invention;

FIG. 5 is a sectional view showing another embodiment of the present invention; and I FIGS. 6 and 7 illustrate two forms of magnetic circuit means of the loudspeaker according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now the present invention will be explained with reference to FIGS. 4-7 which illustrate preferred embodiments of the invention.

FIG. 4 illustrates a direct-radiator loudspeaker, which comprises an annular diaphragm 11 including a vibrating portion 12 having an arcuate shape incross section, such as a shape of a fraction of a circle or an ellipse generated about an axis of revolution which is coincident with the radial center of annular diaphragm 11 (as shown in FIGS. 4 and 5)., and inner and outer support portions 13 and 14. Magnetic circuit means includes a yoke 15 and a ring magnet 16, between which double (inner and outer) concentric gaps are formed. I First and second voice coils 17 and 18 are attached to inner and outer borders or projecting rim portion, respectively, between said vibrating portion 12 and said inner and outer support portion 13 and 14, respectively, and these voice coils are received in said double concentric gaps. Electrical input is applied in such sense to said voice coils that they vibrate the diaphragm in the same phase, depending on the directions of magnetic fields produced at the gaps by the magnetic circuit means and the winding directions of the voice coils. The inner and outer support portions 13 and 14 may be integrally formed with the vibrating portion 12, or they may be made separately and then connected together. In the lattercase, these portions can be made of difierent materials, as desired.

FIG. 5 illustrates another embodiment of the present invention, applied to a horn-type loudspeaker. The construction shown in FIG. 5 is essentially identical with that shown in FIG. 4, and same portions in FIG. 5 are designated by same nu merals as in FIG. 4. The loudspeaker shown in FIG. 5 comprises an annular diaphragm 11 including a vibrating portion 12 and inner and outer support portions 13 and 14, voice coils 17 and 18 and a horn 19. Magnetic circuit means includes yokes 20 and 21, a magnet 22, a center pole 23, and a positioning ring 24 for fixing said yoke 21 in concentric position with said yoke 20 and said center pole 23. 25 designates a spacer ring.

This loudspeaker is essentially identical in construction with that shown in FIG. 4, except the difference of size, thickness, weight, material and shape of the vibrating portion and the support portions of the diaphragm, owing to the difference in type of sonic wave radiation. (In general, the diaphragm must be larger in a direct-radiator type than in a horn type.)

The diaphragm may be made of paper, metal film such as aluminum or duralumin foil, plastic sheet, plastic film, foamed plastics or the like material. The designing .of the inside and outside voice coils and the corresponding gaps in the magnetic circuit means is most important; and the material, diameter, winding width, winding number and impedance, of the voice coils and the flux density in the gaps and thickness of pole of the magnetic circuit means are selected so that the diaphragm may operate under best condition to obtain best characteristic of loudspeaker. The inside and outside voice coils may be designed into unbalanced form in order to meet a particular requirement in the characteristic of the loudspeaker.

FIGS. 6 and 7 illustrate modified forms of the magnetic circuit means for the loudspeakers shown in FIGS. 4 and 5. FIG. 6 shows magnetic circuit means which comprises a central magnet 26, an outer annular magnet 27, a yoke 28 and yokes 29 and 30 attached to the central and outer magnets, said yokes 28, 29 and 30 forming double concentric gaps therebetween. FIG. 7 shows magnetic circuit means which comprises an outer annular magnet 31, a yoke 32, a positioning ring 33, a yoke 34 fixed on the ring 33 and a yoke 35 fixed on the magnet 31, said yokes 35, 32 and 34 forming double concentric gaps therebetween.

The loudspeaker according to the present invention has the following advantages.

1. A light and rigid diaphragm can be obtained, since the vibratingportion of the diaphragm has increased rigidity owing to the arcuate shape in cross section.

2. The vibrating portion of the diaphragm is effectively separated from the support portions by the border driven by the voice coils, so that the vibration of one of them has minimum effect on the other. Accordingly a relatively smooth frequency characteristic can be obtained, without turbulence or distortion owing to the influence of the support portions.

3. The vibrating area can be increased, compared with the conventional dome-type loudspeaker, and a light and strong diaphragm can be obtained with relatively large vibrating area. Accordingly, the efficiency can be also increased.

4. The frequency range of the piston motion of the diaphragm can be materially increased, thereby providing a loudspeaker having high fidelity and non-directional property.

5. The inside and outside voice coils of the diaphragm and the flux density in the corresponding gaps of the magnetic circuit can be so selected that the diaphragm may vibrate under best and balanced state. Thus a loudspeaker can provide good tone with minimum distortion.

6. The inputs to the inside and outside voice coils can be adjusted so that best characteristic amy be obtained. That is, unbalance in operation of the inner and the outer support portions of the diaphragm can be controlled so that the diaphragm may produce perfect piston motion. Such a control cannot be performed in the conventional annular: diaphragm type loudspeaker.

7. A horn-type speaker, to which the invention is applied, has such advantageous properties as large vibrating area, high rigidity, low mass and increased driving force, so that radiation efficiency is high and substantially flat charac teristic is obtained in the higher frequency range.

8. The horn-type loudspeaker, having large vibrating area,

light weight and rigid construction, is particularly suitable to a loudspeaker having a short horn, wherein the size or length of the horn can be made substantially smaller or shorter. Thus the manufacturing of the loudspeaker is facilitated.

I claim 1. A loudspeaker comprising:

a. an annular diaphragm including a single vibrating portion having an arcuate cross section generated about an axis of revolution external to said arcuate cross section and coincident with the center of radius of said annular diaphragm, and inner and outer support portions, said diaphragm further having inner and outer projecting rim portions extending from said annular diaphragm between said vibrating portion and said inner and outer support portions respectively;

b. first and second voice coils attached to said inner and outer projecting rim portions respectively, said first and second coils driving said diaphragm in phase therewith, and

c. magnetic circuit means having inner and outer concentric gaps, said first and second voice coils being positioned within said inner and outer concentric gaps respectively. 

1. A loudspeaker comprising: a. an annular diaphragm including a single vibrating portion having an arcuate cross section generated about an axis of revolution external to said arcuate cross seCtion and coincident with the center of radius of said annular diaphragm, and inner and outer support portions, said diaphragm further having inner and outer projecting rim portions extending from said annular diaphragm between said vibrating portion and said inner and outer support portions respectively; b. first and second voice coils attached to said inner and outer projecting rim portions respectively, said first and second coils driving said diaphragm in phase therewith, and c. magnetic circuit means having inner and outer concentric gaps, said first and second voice coils being positioned within said inner and outer concentric gaps respectively. 